Mentor Trait?
One of the traits you can buy with aspiration points is Mentor. Apparently it lets your sims mentor other sims when they reach level 10 of a career, but my sims have always been able to do that anyway...
Forum Discussion
I use it quite a lot, for my parents to mentor their teens. The teens get a "expertly mentored" bonus trait (or something along those lines), and they seem to build those skills much quicker than usual. It does only seem to work for specific skills, like logic or fitness, or musical instruments though.
